Liquid crystal display devices are devices performing display by controlling optical characteristics of light emitted from a light source using a liquid material and the like charged into a liquid crystal display panel, and have been widely used in various fields, using features such as slim profile, lightweight, and low power consumption.
The liquid crystal display panel (liquid crystal display element) as a major member of such a liquid crystal display device generally has a structure in which liquid crystal materials are charged between a pair of glass substrates. In order to keep a gap (distance) between the two glass substrates, a spherical spacer mainly made of plastic or an inorganic material is used.
A wet scattering method of spraying a dispersion liquid into which spacers are dispersed and a dry scattering method using inert gas such as nitrogen have been commonly used as a method of disposing the spacers on the substrate. However, in these scattering methods, the spacers are randomly disposed on the substrate surface. Therefore, the spacers are disposed also in a display region, which has an adverse effect on display characteristics.
Accordingly, various methods of disposing spacers only in a non-display region have been investigated. As one of such methods, a technology of forming spacers at an objective position by a photolitho process using a resin material, not by scattering the spherical spacers has been proposed. However, such a resin spacer formed by photolitho process is inferior to the plastic spacer in terms of uniform control of a cell thickness because the resin spacer varies in the thickness direction, in comparison to the plastic spacer and the like. In addition, the formation of the resin spacer using the photolitho process significantly increases costs in comparison to the method of scattering the plastic spacers. In such a respect, there was room for improvement.
A method of selectively disposing spherical spaces in a non-display region has been also investigated. A method of disposing spacers on the entire substrate surface and then removing the spacers disposed in a display region, or a method of printing spacers in a non-display region using a printing method has been proposed, for example (for example, referring to Patent Documents 1 and 2). However, the former method needs an addition step such as a step of removing the spacers in a display region, and in the latter method, a screen for printing gets into contact with a display region subjected to an alignment treatment and thereby alignment of liquid crystal materials are adversely influenced. In such a respect, there was room for improvement.
Methods of scattering a dispersion liquid prepared by dispersing spacers into a dispersion medium or a liquid material for spacers using a ink jet device have been investigated as a method of disposing the spherical spaces only in a non-display region simply and without contact (for example, referring to Patent Documents 3 to 5). However, liquid crystal display devices need to secure a pixel region (display region) which is as large as possible, and a non-pixel region (non-display region) becomes narrower year by year. Therefore, not all of the spacers are disposed inside the non-pixel region actually, even if a high-accuracy ink jet (IJ) device is used. For this problem, it has been proposed that deterioration in display characteristics is suppressed as much as possible even if the spacers enter the pixel region, by coloring the spacers themselves or subjecting the spacer surface to an alignment treatment on the assumption that the spacers are out of the non-pixel region. However, there is concern that such an additional step of treating the spacers themselves increases the price or has an adverse effect on the reliability.
A method of using a depression between electrodes or between colored layers (above a light-shielding layer) has been proposed (for example, referring to Patent Document 6). However, the Patent Document 6 makes no new proposal of formation of such a depression, and a depression generated by pixel formation is mainly used in the same configuration as a previous configuration. Therefore, in this method, it is difficult to perfectly dispose the spacers inside the non-display region.
In addition, the Patent Document 6 proposes that the substrate is directly processed to have a more deep depression, but does not disclose the details. The method of directly processing the substrate may be an effective method for display elements having a simple configuration such as those in passive matrix type. However, sufficient effects can not be obtained in substrates including a switching element such as a thin film transistor (TFT). This is because that, in the TFT array substrate that is a multilayer substrate formed by stacking various films on a glass substrate, even if some irregularities exist on the glass surface, the irregularities are planarized during the stacking process. If the depression on the glass substrate is formed to be larger in view of this planarization, the strength of the glass substrate is reduced. Glass substrates for processing recently become larger, and therefore it is a large disadvantage in terms of yield that the strength of the glass substrates themselves is reduced due to formation of the depression on the substrate.
As liquid crystal display modes other than commonly used TN mode, Multi-domain Vertical Alignment (MVA) display mode and In-Plain Switching (IPS) display mode in which liquid crystals are driven in a lateral direction (in a direction parallel to a substrate surface) have been widely used for improvement in view angle characteristics of liquid crystal display, recently. In the MVA display mode, a linear (rib-shaped) projection structures are formed on a color filter (CF) substrate for alignment control, and slits are provided with pixel electrodes on a TFT substrate for alignment control (for example, referring to Patent Documents 7 and 8). The rib-shaped projection structures on the CF substrate are disposed also in a non-pixel region, and depressions are not formed uniformly, which is different from those on a normal CF substrate. On the TFT substrate, the pixel electrodes have slits, and the slits as well as the region between the pixel electrodes have the depression shape. Therefore, spacers may be disposed not only between the pixel electrodes but also inside the slits. In the IPS display mode, as in the case of the TN mode, it is difficult to dispose every spacer inside the non-display region because of a relationship between ejection accuracy of an IJ device and width of the non-display region.
Accordingly, in the existing substrate configurations, it is difficult to selectively dispose the spacers inside the non-display region.    [Patent Document 1]    Japanese Kokai Publication No. Hei-05-333346    [Patent Document 2]    Japanese Kokai Publication No. Hei-05-303102    [Patent Document 3]    Japanese Kokai Publication No. Sho-57-58124    [Patent Document 4]    WO 97/36205    [Patent Document 5]    Japanese Kokai Publication No. 2002-372717    [Patent Document 6]    Japanese Kokai Publication No. 2004-145102    [Patent Document 7]    Japanese Kokai Publication No. 2001-83517    [Patent Document 8]    Japanese Kokai Publication No. 2001-83522